For purposes of this description, there are two broad categories of integrated circuit devices: (1) single mode devices and (2) multiple mode devices. In the case of a single mode device, there is generally a specific hook up arrangement which must be adhered to when connecting the leads of the chip to external circuitry. The multiple mode device, however, will allow one of two or more such hook up arrangements, depending upon the requirements of a specific application. It is this latter type of device to which the present invention pertains.
By way of example we shall assume that a certain integrated circuit chip is useful for processing signals that are produced by a microprocessor (MPU) and transmitted to the chip over bus lines. The MPU may be either of two well known units: one selected from the Motorola Model 6800 series and the other selected from the RCA Model 1800 series, both of which produce data signals and address signals. The RCA MPU provides data signals on one output line and address signals on another output line, each output line being completely independent of the other. Therefore, provision is made for the chip to accept these two MPU outputs on two separate bond pads, one of which is connected to the data bus of the integrated circuit via a data latch which is latched open to permit passage of data and the other of which is connected to an address store circuit through an address latch which is latched open to permit passage of address signals. The Motorola MPU, on the other hand, provides the low order bits of the address alternately time sliced with data signals on a single output line. This output must therefore be impressed on two separate bond pads of the chip, the first of which is, as before, connected to the data bus via a data latch and the second of which is connected to the low order bits of the address bus via an address latch. To permit the integrated circuit to properly interface with the Motorola MPU, a latch enable signal must be supplied to the integrated circuit for the data latch thereby disabling the data bus at times when address signals appear on the output and for enabling the data bus at other times. Similarly, another latch enable signal must be provided to enable the address latch and thereby disable the address bus at times when data signals appear on the output and to enable the address bus at other times. The above hypothetical example very briefly describes an integrated circuit chip having two modes of operation, one being enabled for interface with RCA MPU and the other being enabled for interface with the Motorola MPU. Selection of the Motorola mode is automatically effected by impressing the single output line on the two appropriate bond pads of the chip.
When selecting a particular function or operating mode of a multi-function device a variety of hook up arrangements may be used including electrically connecting two or more bond pads together, omitting specific connections, and transposing certain connections. When two or more bond pads must be connected together, as in the Motorola case described above, it is conventionally accomplished by connecting each pad individually to its respective lead by a connector wire, then tying the two leads together with a jumper wire outside of the device package. Such a procedure requires that two connector wires and two leads be provided for each pair of pads that must be connected together. This renders the device somewhat less reliable because of the additional connections, four internal bond points and two external connections, and reduces the number of functioning leads that may be brought out of the package. Another method of connecting two or more pads together, which is less commonly used, is to connect each pad individually to a common lead by a pair of connector wires. This, of course, necessitates the making of two connections on a single lead which requires that the lead be sufficiently wide to accommodate the two bond points. Here again there are two connector wires and four bond points. What is desired is the capability of electrically connecting a single lead of the package to two or more bond pads at a single bond point using a single connector wire.